Inkjet printers form printed images using one or more printheads, each one of which includes an array of inkjet ejectors. A controller in the printer operates the ejectors to form printed images that often include both text and graphics and may be formed using one or more ink colors. Some inkjet printers move print media, such as paper sheets, envelopes, or any other article suitable for receiving printed images, on a belt past one or more printheads to receive the ink drops that form the printed image. Many printers that use belts to transport print media use a vacuum plenum and belts that have holes to generate a suction force through the surface of the belt. Each print medium engages a portion of the holes on the surface of the belt and the suction force holds the print medium to the surface of the belt to prevent the print media from slipping or otherwise moving relative to the surface of the belt as the belt moves through the printer. Holding each print medium in place relative to the surface of the moving belt enables the printer to control the timing of the operation of printheads to ensure that the printheads form printed images in proper locations on each print medium and ensures that the print media do not cause jams or other mechanical issues with the printer. In large-scale printer configurations, the belt often carries multiple print media simultaneously.
One problem with belts that carry print media over a vacuum plenum is that the print media often do not completely cover every hole on the belt. For example, as a belt carries two or more print media, a gap between sheets of consecutive print media can include holes exposed to the vacuum plenum. The relative locations of gaps on the belt often change between print jobs that use print media of different sizes. The suction force of the vacuum plenum draws air through the exposed holes near the edges of the print media, which produces airflow. In regions around the printheads, the airflow can affect the paths of ink drops as the ink drops travel from the printhead to the surface of the print medium, which can reduce the accuracy of drop placement and degrade image quality, particularly near the leading and trailing edges of the print media. For example, FIG. 3 depicts printed images produced by a prior art printer where text printed near a trailing edge of a document exhibits degraded image quality due to the airflow near the printhead. Consequently, improved media transport systems that provide suction force to hold print media in place while reducing or eliminating the negative effects of airflow due to exposed holes near printheads in the printer would be beneficial.